This invention relates to the field of communications apparatus having the capability of switching from an integral to an external antenna and, more particularly, to such capability including integral impedance matching.
Many kinds of apparatus are known which require switching from one antenna to another and there are many types of interconnect arrangements which will switch automatically as, for example, when a portable device is inserted into a higher powered unit in a vehicle. In such a case, the portable antenna may be either inadequate or too shielded by the vehicle body for transmission and reception over longer distances. Such an arrangement is shown in U.S. Pat. No. 3,946,390, issued Mar. 23, 1976, and assigned to the same asignee as is the present invention. In that arrangement, a coaxial connector on the end of a coaxial cable activated a conductive plunger which disconnected the integral antenna from the radio circuit and connected an external signal source from an external antenna to the radio circuit. Neither the integral antenna nor the cable connection to the radio circuitry were of a coaxial configuration, and the switching arrangement did not require shielding at the frequencies used (300 MHz). At higher (UHF) frequencies, both the shielding and mismatch problems become acute and a different switch/connector arrangement is required.